The invention relates to a chair mechanism, in particular for a rotatable office chair with a pneumatic spring which is arranged vertically in the under-frame and is intended for adjusting the height of the seat. The chair mechanism causes the seat panel to be lowered synchronously with the rearward inclination of the backrest, which the user initiates by shifting his/her weight.
Office workers spend most of their working day in a sitting position. Staying in a writing position, in which the body is bent forward to a pronounced extent, over a number of hours at a computer workstation results in considerable straining of the skeleton, the muscles and the tissue of the back and the neck region. As a result, many attempts have been made to improve the geometry of chairs, and the mechanisms thereof, in order, in accordance with the respective sitting posture, to relieve the strain on the user more effectively. A decisive step in development was made by synchronizing mechanisms, where, with the adjustment of the backrest, via lever and articulation connections, the seat follows synchronously and, with each inclined position of the backrest, an ergonomically adapted position of the seat surface is established. Such a synchronizing mechanism is disclosed in CH-A-629 945. This mechanism allows the user to move out of the upright working position, by shifting his/her body weight in the rearward direction and applying pressure against the backrest, which is spring-mounted in a damped manner, into a rearwardly inclined, relaxing position, e.g. during a lengthy telephone call. The seat follows the inclining backrest, with the result that a rearwardly inclined, strain-relieved, resting position is achieved for the user. These chairs allow easy and frequent changeover into a relaxed user position.
It is usually the case, however, that office work can only be done in a forwardly bent position, rather than in a relaxed, rearwardly inclined position, in order to be in contact with the documents on the desk. In order to reduce the pressure of the seat against the lower leg and to force the user to straighten his/her spine, mechanisms in which, in the forwardly inclined position, the front seat surface is lowered as a result of the shift in weight are proposed. Moreover, attempts have been made, by specific shaping of the backrest with a lumbar support and at least simultaneous raising of the rear seat surface, to prevent the harmful rearward-rolling movement of the pelvis and a curved back. However, the backrest only provides support if one is seated properly in the chair and has definite contact with the backrest. In reality, the back region is not given support since one is usually seated in the vicinity of the front edge of the chair. EP-B-0 592 369 has thus proposed a synchronizing mechanism where, in the case of forwardly bent and upright sitting positions, the seat is lowered in the forward direction and, in the case of a shift in weight, the user slides into a rearwardly inclined, relaxing position.
The springs used are of critical importance for the functioning of a chair mechanism. In order to execute the synchronized movement between the backrest and seat panel, use is frequently made of pneumatic compression springs which, in order to improve the kinematics, are often coupled to helical compression springs (e.g. CH-A-629 945). However, pneumatic compression springs involve a number of disadvantages: they increase the cost for the overall chair to a considerable extent and, in order to achieve a favorable movement sequence, have to be coupled to mechanical springs, which further increases the cost and complexity of the design. Furthermore, the wear on the seals means that pneumatic compression springs only have a limited service life. WO-A-92/03072 has thus proposed using a mechanical spring in the form of a torsion bar for the spring mounting during the synchronized movement.
WO-A-93/25121 proposes using a rubber spring with an embedded steel core and an outer steel casing, the inner steel core being subjected to torsion. In the normal position of the seat, the use of such a rubber spring provides too low a level of stiffness, as a result of which this sitting position does not have the full amount of stability desired. This is not improved in any way by the envisaged positioning of the axes of rotation, i.e. an approximately central, rocker-like suspension of the seat panel and the articulation of the seat panel in the rear region.
With the number of computer workstations constantly increasing, one is increasingly forced into an upright sitting position, with the neck region permanently tensed, in order to view the screen. This means a change in the typical working position for many people and, consequently, different requirements have to be met by the mechanisms of a chair in order to optimize the kinetic behavior of the latter. The prior-art synchronizing mechanisms are advantageous for users whose work allows them to change position frequently, namely between forwardly bent, upright and rearwardly inclined sitting positions. However, the known designs are still not ideal for individuals who have to sit permanently at a computer workstation.
The object of the invention is thus to provide a mechanism which provides, as a permanent working position, a rearwardly inclined sitting position in which the body is largely free of strain and which has a wide opening angle between the seat surface and rear surface. In the front sitting position, it is necessary to realize effective support for the lumbar region, while, in the rearwardly inclined sitting position, partial sinking into the chair is intended to provide a relaxed sitting position without the eye-contact angle having to be changed to any significant extent. In the relaxed, rearwardly inclined sifting position, the mechanism and the overall chair construction are intended simultaneously to allow a certain capacity for movement, and to provide noticeable support for the shoulders, for the user in the chair. The seat and the backrest are intended to be height-adjustable. Also desired is the capacity for regulating the seat depth and the intensity of the lumbar support as well as an adjustable neck support. The intention is for the chair to be mass-producible efficiently and cost-effectively.
Finally, the design must correspond to current tastes.
The chair mechanism of the seat rests on an underframe with a basexe2x80x94usually a standard five-armed star-shaped basexe2x80x94which is positioned on the floor, and a vertically arranged pneumatic spring with a telescopically extendible piston rod for adjusting the height of the chair. The seat is positioned on the piston rod, by way of the seat support arranged at the bottom, as a structural unit. Extending through the seat support is the horizontal main axis of rotation with the torsion spring, preferably a rubber spring, positioned along the same. Acting on the torsion spring is the rear support which can be pivoted about the main axis of rotation, counter to the resistance of the torsion spring. The chair also has a seat panel for receiving a seat cushion, possibly with the interposition of a cushion support. The seat panel, on the one hand, is articulated on the rear support along a horizontal rear axis of rotation and, on the other hand, is connected to an articulation along a horizontal front axis of rotation. The articulation is connected to the seat support along a horizontal fixed axis of rotation. The rear support and seat panel execute synchronous changes in position as they are pivoted between a vertical position and an inclined position.
The essence of the invention is that provided parallel to the torsion spring, and with accumulative effect in relation to the resistance of the torsion spring, is a further mechanical spring. The parallel spring is preferably a helical spring which can be separated into two symmetrically arranged parts. Another factor which is critical for the properties of the mechanism is constituted by the positions of the axes of rotation, which are all located beneath the seat panel. The front axis of rotationxe2x80x94as connection between the seat panel and articulationxe2x80x94is provided in the vicinity of the front edge of the seat panel, it being possible for the front axis of rotation to be pivoted radially over part of a circle about the fixed axis of rotationxe2x80x94as connection between the articulation and seat support. The rear axis of rotationxe2x80x94as connection between the seat panel and rear supportxe2x80x94is located in the vicinity of the rear edge of the seat panel, it being possible for the rear axis of rotation to be pivoted radially over part of a circle about the main axis of rotation. The main axis of rotation is positioned between and beneath the front and the rear axes of rotation.
The fixed axis of rotation should preferably be located above the plane of the main axis of rotation and, in the vertical position of the chair, the front axis of rotation should be more or less vertically above the fixed axis of rotation. In the maximum inclined position, the rear axis of rotation should be capable of being lowered at least into the vicinity of the plane of the main axis of rotation. In the vertical position of the chair, the front axis of rotation is arranged in front of the fixed axis of rotation, in relation to the main axis of rotation. Starting from this chair position, the ratio of the horizontal spacing between the fixed axis of rotation and main axis of rotation and between the main axis of rotation and the rear axis of rotation is in the region of 1:2. In the maximum inclined position, the seat panel assumes a sloping position in the region of 15xc2x0.
The actually conventional torsion spring comprises the inner steel core, the rubber layer which is firmly applied to the steel core, and the outer steel casing which is firmly applied to the rubber layer. Extending through the steel core, along the main axis of rotation, is a polygonal through-passage into which a polygonal carry-along rod of complementary profile is inserted. The carry-along rod has its outer ends positioned in the free ends of the rear support, the latter being designed in the form of a fork with two support arms and said free ends being provided with a polygonal socket. Fastened on the outer steel casing of the torsion spring is an adjustable drawing element for adjusting the prestressing of said spring.
The parallel spring is arranged along the front axis of rotation and is supported, as a helical spring, beneath the seat panel by way of one end, while the other end of the helical spring is fixed on a pretensioning bolt. The pretensioning bolt is located along the front axis of rotation, is firmly inserted into the articulation and is positioned rotatably in front articulation extensions provided on the underside of the seat panel. There are in each case two articulations, pretensioning bolts, helical springs and pairs of articulation extensions, arranged symmetrically in relation to the torsion spring.
The rear support, between its two support arms, has a bearing bushing which is arranged beneath the seat panel, through which the rear axis of rotation extends and on which, positioned on an axial rod, rear articulation extensions provided on the underside of the seat panel are articulated. Above the seat panel, the two support arms are combined in a U-shaped guide which serves for receiving a backrest in a height-adjustable manner. The seat support comprises first of all the central sleeve body, with the main axis of rotation running through it, for receiving the torsion spring. The sleeve body is adjoined at the rear by the plug-on flange with its conical bore which runs along the vertical axis and is intended for positioning on the piston rod of the pneumatic spring. The bearing flange adjoins the front of the sleeve body. Said bearing flange has a through-passage bore which runs along the fixed axis of rotation, parallel to the main axis of rotation, and is intended for receiving an axial rod on which the articulations are arranged, on either side of the bearing flange. The sleeve body has a cutout for fitting the drawing element on the outer steel casing of the torsion spring.
The backrest comprises first of all the bottom, base member for insertion into the guide on the rear support, and an upwardly extending central member which adjoins the base member. Two lumbar extension arms which extend out horizontally in arcuate form symmetrically between the base member and central member serve for retaining and tensioning a flexible back shell. Two supporting arms which open in the form of a Y extend out from the top of the central member. The free ends of the lumbar extension arms have through-passage bores for fastening a back shell, while the ends of the supporting arms are positioned in pockets provided on the back shell. An inclination-adjustable headrest may be fitted on the backrest. The tensioning of the back shell in the lumbar region can be adjusted in a variable manner by means of eccentrics arranged in the lumbar extension arms. The back shell is spanned by a covering to the full extent on the user side and partially on the rear side, a shaped pocket and quick-action closures being provided in order to fix the covering. The headrest can be adjusted to a desired setting angle and selectable height.
The essential advantages of the chair mechanism according to the invention lie in the large opening angle between the seat panel and backrest in the inclined position, the adjustable reaction capability of the chair when the user shifts his/her weight, and the flexible, compliant seat shell, with the result that it is possible to take up the relaxed inclined position as a permanent working position. The intensity-adjustable lumbar support, the selectable height adjustment of the backrest and a headrest which can be adjusted in a variable manner in terms of setting angle provide a high level of sitting comfort, which is particularly important when one is working with a keyboard and at computer workstations. In the inclined position, the front edge of the seat panel is lowered and the entire seat moves in the rearward direction to a considerable extent. The optimum seat level thus provides the user""s body with effective support for his/her back and shoulders without eye contact with his/her screen being lost and the neck muscles being strained. The preferably mesh-like covering of the back shellxe2x80x94and possibly also of the head cushion and armrestsxe2x80x94gives pleasant seat-climate conditions and a decorative effect.